Polyolefin resins are used to prepare the insulation for wires and cables as well as components such as buffer tubes for optical fibers. When the wires and cables are used for telecommunications, the insulation must comply with requirements for thermal oxidative stability (e.g. Telecordia Specification GR-421). Thermal oxidative stability can be determined by measuring the oxidative induction time (OIT) of the resin with differential scanning calorimetry (DSC). DSC is used to measure the amount of time the polymer or resin can be maintained at an elevated temperature, e.g. 200° C., before significant signs of oxidative degradation are observed. A second test that is set forth in GR-421 is to measure the OIT of the insulation, once the insulation has been “aged” in water blocking filler for an extended period of time.
One approach of improving the oxidative stability of a resin is to add an antioxidant, such as IRGANOX® 1076 or 1010. A problem can occur, however, when the amount of antioxidant exceeds its solubility in the polyolefin resin. This problem of solubility is even more pronounced for “aged” resins. Because “aged” resins require higher concentrations of the antioxidant to meet the requirements of GR-421. Moreover, high concentrations of an antioxidant can also impair the dielectric properties of the polymer. Electrically active species in the antioxidant, e.g. functional groups, can lead to losses in the dielectric strength of the insulation. Furthermore, when high enough electric fields are applied across insulation, burning or vaporization of the insulation can occur. High concentrations of antioxidant can also lead to attenuation.
Another problem is that water-blocking agents extract the antioxidant from the polyolefin resin. When wires and cables are bundled together in a conduit or a tubular housing, a water-blocking agent (e.g. grease) is often introduced into the housing. Water-blocking agents are used to reduce or eliminate water migration paths into the housing. When a significant amount of antioxidant is extracted, surface deterioration can result in attenuation, cross-talk, or premature catastrophic failure, see e.g., U.S. Pat. No. 7,238,765.
Since optical fibers are relatively fragile they require mechanical support or protection, e.g. buffer tubes, reinforcing elements, during the handling and installation of the optical fiber cables. Extraction of the antioxidant by water-blocking agents from the buffer tubes, slotted cores, spacers, reinforcing elements etc. can also affect the reliability of optical fiber cables. The extraction of the antioxidant can lead to the deterioration of the mechanical properties of the resin, e.g. modulus of elasticity, elongation at break etc. As the polyolefin resin becomes more brittle, extrinsic attenuation can result from micro-bending, e.g. tensile force, of the optical fibers. Attenuation or signal loss can occur when light is refracted outside of the optical path. The degradation of the polymer material can also lead to the phenomena of tracking, in which paths or areas of erosion in the resin extend until the resin is ruptured.
It would be useful if the polyolefin resin used to prepare coatings for wire and cable and components could provide sufficient thermal oxidative stability at lower antioxidant concentrations. Moreover, it would be useful if the antioxidant in the resin is less susceptible to being extracted into the water-blocking agent, especially at elevated temperatures.